1. Technical Field
The present invention relates to a binder resin suitable for the use in the development of an electrostatic latent image formed by electrophotography or electrostatic recording method with a developer. The present invention also relates to a particulate resin dispersion produced from the binder resin and an electrostatic image development toner produced therefrom. The present invention further relates to an electrostatic image toner comprising the electrostatic image development toner and an image forming method.
2. Related Art
In recent years, with the rapid spread of digitization technique, it has bee required to enhance the quality of image outputs such as printed image and copied image for users at ordinary home, office and publishing field. On the other hand, in order to realize a durable society, there has been a growing demand for reduction and saving of energy required for enterprise activity and products as its results. Then, in image forming methods involving electrophotography or electrostatic recording, too, it is necessary that the electric power required at the fixing step, which consumes much energy, be saved and the step of producing products from photographic materials be effected with low environmental burden. As a countermeasure against the former problem there may be proposed an approach involving the lowering of the toner fixing temperature. By lowering the toner fixing temperature, the required electric power can be saved. Further, the time required until the temperature at which the surface of the fixing member is reached, i.e., so-called warming-up time can be reduced and the life of the fixing member can be prolonged.
As a toner binder resin there has heretofore been widely used a vinyl-based polymer. In order to obtain offset resistance, it has been proposed to use a high molecular polymer. However, since a high molecular vinyl-based polymer has a high softening point, it is necessary that the temperature of the heat roller be predetermined higher to obtain a fixed image with an excellent gloss. This is contrary to the requirement for energy saving.
On the other hand, a polyester resin has a rigid aromatic ring in its chain and thus has flexibility as compared with vinyl-based polymers and can be predetermined to have a lower molecular weight when the same mechanical strength is needed. Further, a polyester resin can be easily designed as a low temperature fixing resin as compared with vinyl-based binder resins from the standpoint of entangling of molecular chains and critical molecular weight. Thus, a polyester resin has been widely used as a binder resin for energy saving toner.
It is normally necessary that the polyester polycondensation method involve reaction at a temperature as high as more than 200° C. with stirring by a great dynamic power under highly reduced pressure for 10 or more hours, causing the consumption of a large amount of energy. In order to provide the reaction facilities with durability, a huge facility investment is often needed.
On the other hand, a study has been reported on the conversion of the high energy-consuming type method for producing polyester to a low energy-consuming type method by the use of catalysts having activity at low temperatures.
A polycondensation catalyst normally forms an intermediate with a monomer during the reaction to lower the activation energy, exerting an effect of accelerating the ester synthesis reaction. Brönsted acids, which have long been known to have catalytic activity, are similarly used in the polycondensation at low temperatures or under water. A Brönsted acid type catalyst is determined by the balance of an acid having a catalytic action with a lipophilic hydrophobic group moiety. In other words, the acidity of the catalyst governs the direct catalytic capacity and the hydrophobic group moiety governs the compatibility of the catalyst with monomers or oligomers and polymers thus produced to affect the progress of the reaction.
It has been heretofore occasionally practiced to use a Brönsted acid catalyst for polycondensation. However, neither the structure of the catalyst nor the invention concerning the use of a Brönsted acid catalyst having a plurality of specific structures have been reported.
Brönsted acid type catalysts which have heretofore been studied are materials having a general-purpose sulfonic acid groups such as sulfuric acid, p-toluenesulfonic acid and dodecylbenzenesulfonic acid. Neither the combination of these Brönsted acid type catalysts with monomers having adaptability to toner nor the structure of these Brönsted acid type catalysts themselves have been optimized.
Moreover, a Brönsted acid catalyst tends to deteriorate its reactivity when present in a large amount. This tendency becomes remarkable particularly with Brönsted acids having a long straight-chain aliphatic acid called soft type. In other words, when a Brönsted acid catalyst is used in an amount exceeding a certain proper catalytic amount, the reactivity shows a rapid drop, causing the occurrence of a phenomenon such as stop of the rise of molecular weight. In the case where the proper amount of the catalyst to be used is limited and a slight change of the amount of the catalyst affects the progress of the reaction, if a large-scale continuous production is assumed, the physical properties of the products vary from batch to batch. Further, very close process design and control are needed, causing the deterioration of productivity.